Get an array of users for a given role id.

drupal-users-by-role-id.php

/**
 * Get an array of users for a given role id.
 * @param int $rid - The role id
 * @return array
 */
function users_by_role_id($rid)
{
  $users = array();
  $uids = array();
  $query = db_query("SELECT uid FROM users_roles WHERE rid = :role_id", array(':role_id' => $rid));

  while($uid = $query->fetchCol('uid')) {
    $uids[] = $uid;
  }

  if ( ! empty($uids)) {
    $users = user_load_multiple($uids);
  }

  return $users;
}